Summary: CNAM Special Condensed Matter Colloquium
4pm, May 12th
, Room 1201
l/f Flux Noise in Qubits and SQUIDs: The Saga Continues
Professor John Clarke
Department of Physics, University of California, Berkeley
&
Materials Sciences Division, Lawrence Berkeley National Laboratory
At millikelvin temperatures, superconducting flux qubits (quantum bits) and SQUIDs
(Superconducting QUantum Interference Devices) both suffer from intrinsic magnetic flux
noise. The noise power spectrum scales as 1/f
, where f is frequency and is
approximately unity. Low-frequency flux noise enhances decoherence in qubits and
reduces flux resolution in SQUIDs. Remarkably, all devices show approximately the same
level of noise, a few µ0Hz-1/2
at 1 Hz; 0 is the flux quantum. The magnitude of the flux
noise scales only weakly with the area of the device, ruling out external uniform magnetic
field noise as the source. A model based on the random flipping of surface electrons
between up and down states is consistent with the observed weak dependence of the noise
on area. This model requires an areal electron density of about 5 × 1017